1-36 CAUTION Because vacuum tubes become hot and most are made of glass, use caution while removing or replacing them. Use vacuum tube pullers or at least wear some type of hand protection. Wavelength Wavelength is the distance in space occupied by one cycle of a radio wave at any given instant. If a radio wave could be frozen in time and measured, the distance from the leading edge of one cycle to the leading edge of the next cycle would be the wavelength. Wavelength varies from a few hundredths of an inch at the high frequencies to many miles at extremely low frequencies. Common practice is to express wavelength in meters. The Greek letter lambda () is used to signify wavelength. Formulas for wavelength, period, and velocity are shown below. Wavelength formula: Frequency formula: You can find more information on wavelength, frequency, period, and velocity in NEETS, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas.